9 Sex Determination and X Chromosome Dosage Compensation

Abstract

I. INTRODUCTION
The choice of sexual fate is an early developmental decision with far reaching consequences. In Caenorhabditis elegans, this decision not only specifies the overt sexual characteristics evident in adults, but also sets the level of X chromosome gene expression in all somatic cells throughout development, starting at the 30-cell stage. The sex determination decision itself must be made with considerable fidelity, despite the fact that only a twofold difference in X chromosome number triggers this major developmental event.

Studies during the last two decades have identified many of the genes in the complex regulatory hierarchy that determines sexual fate in C. elegans, stemming from those that comprise the sex-determining signal itself to those that control sexual dimorphism and X chromosome expression. Molecular mechanisms underlying many aspects of sex determination and differentiation have also been revealed. Indeed, studies of sex determination in C. elegans have proven it to be a rich source of information concerning the molecular nature of developmental decisions and how they are regulated. These studies have intersected work in many areas including transcriptional regulation, translational regulation, RNA processing, signal transduction, and chromosome structure.

This chapter summarizes our current understanding of the genetic and molecular basis for sex determination and the related process of dosage compensation. The extensive information obtained will facilitate future efforts to tap the enormous potential that this system holds for addressing fundamental biological and biochemical questions.

II. SEXUAL DIMORPHISM
C. elegans has two natural sexes, XO males and XX hermaphrodites. The hermaphrodites are...